Corrosion preventing means



20, 1953 c. M. OSTERHELD CORROSION PREVENTING MEANS 2 Sheets-Sheet 1 Filed May 28, 1947 L.. 3 f wxm I INVENTOR CL'A R/( Us rsnfia 12 BY 'fl/zy ATTORN Y QcLZO, 1953 c. M. OSTERHELD CORROSION PREVENTING MEANS 2 Sheets-Sheet 2 Filed May 28, 1947 INVENTOR CL/mk Oman/2&1: BY m ATT 0R EV corrosion and preventing cor Further, it is proposed 'to provl with respect to operating '"ef fi ci (r life, and cost of initial 'instal l'ation "and rep merit her; will ensure' ful-l protection corrosion protection for a tank :with a sacrificial-anodewhich" Patented Oct. 20, 1953 PATENT OFFICE magenta PREVEN ING MEANS Clark M; Oste'rheld, Stougliton, Wis. assignor to McGraw Electric Company, Elgin, 111., ammogation of Delaware Amalia May 218; 1947, Seri l Na 50,900

l 14 Glaims.

My mvehutn relates toierrous rxfeta-l storage tanks, and more particularly to hot water storage tanks such as used for doi-r'iestic purposes; As is Well known, hot vv'jati" is frec1uen tly witti -dramn from such tanks and replaced by incoming'c'oid Water; V V. a f One of the objc'tsfo f my inventio; to provide a relatively simple hut highly-efficient rfnieans for preventing c'c'r'rosioiikif the nside surface-of a hot water tank when the same is filled over extended periods withwater,

Anothe'i' 'ob'jetoj my vention'is toprovidea corrosion-preventing means and method that shall =be simple and easy "install; that shall con tinue in operating condition 'over extended pee riods of time and use of iNhichsha'll result in reducing 'tliefinitial cost ofthe tank-itself; V

Another obj ect of the invention to 'p'r as means in a metallic hotwater tan'l; a ficial anode from which; -withoutthe n es 'typ'f an externally suppliedgyoltage, a m; tive cur rent W111 haw through the wat If s all areas or the tank, the g asse ats its anode of a material'which'is I a in ee An ther o ject b m ii t i ionvis zicflii'rblrde rate 1 of dissociation of the scorros1 n preveritjing .mem'ber. Morejparticularlm it provide controhmeans' that,'"wh

.pr n mi operative life of the corrosion-preve ntin e conjunction with a prdtective-sacriii a1 anode, V in the electrical connection between theJanelle and the tank, it --is'"proposeti "to incorporate an electrical resistance element of suitable ohm ge zto prolongthelife of the anodebut notso large as lto re'ducethe prtteem urrenp now to the 'tank below -the -m'inimum'-require* d"to ensure com -plete:tank protection.

A "further object oi-my inventionis uniformity of' protection against "corn throughout -the entire surface-areathe ta 1;; :A"ifurther obiect=ofthe inventionis tf'pro v 1 hd hwater satisfactorily under varying condi affect the amount -of 'th *-'protective;curren between :the anode and the tank, ;and-to -pi vide water with changes in temperature, which may W111 erate b o siderable n Wate a ks b prev ine res s anc el ment hav n an ma e h ch is onstant. or s b nt so nd tem era re han es an which I t element w l m telii lr le n u t at ns i th rot t cur,- rent with changes in the water resistance. 7 Other objects .of my invention will either be apparent from a deSCiiption of several forms of devices embodying my invention or will he pointed out in the course of such description and particularly in the appended claims. I

It has long been known that water used for or hea i unie s or ,l q dome t c o oithr similar us 'swniams fier s bstances and that it may ei her be slightly acid (trace of hydrochloric acid), alkali containing (such as sodium hydIQXidc) or saline (such as magnesium chloride). When such Water is contained in a tank it will, of course, under certain conditions, constitute an electrolyte and may have a deleterious action and effect upon the inside surface of the tank, particularly so if the tank consists of a ferrous metal, which in itself may contain impurities of the kind' usually found in iron, Various ;methods of protection against such action have been proposed.

The most common prior n ethod of protecting ferrous rnetal Water tanks against deterioration dueto ater conditions has been to coatlthe insidesurface of th tarik with zinc. However, such method is far frorn'reliable for reasons hereafter nt eyten i ea sn iv-aswen.

Ihave found that by the use of my invention; it is unnecessary to provide a zinc coating on the insidesurface of a tan}; adapted to contain riomestic water, that is, .toflbe filled over extended pcr odsuq 't me. th rwa i tse of co r e-bein changed as withdrawals from the task occur in qinary .use- In such cas t t k ould h made of relatively purejiro'ni, now eyajilahle on h mar et rfl wcv r the' i v n i l perat v in a zinc lined tank, and with advantages over the use .of either su ch protective coating or the ve tio a one as h rea t ex l ined,

11 m m -ininti i re e tiveiof vvi eth the'inside surface ofthe tanl is inc coa ed. or; t qermsi h rreniin mam:

her comprising a rod or other block of a material 'a domestic hot water tank will be that pole or terminal from which an electric current flows through the water electrolyte to the other pole or terminal of the circuit, which other pole or terminal is the cathode'and in this case is the tank itself. In other words, the anodic member is the one which is dissolved or attacked by the electric current caused by the electrolyte engaging two dissimilar electric conducting materials.

The sacrificial anodic member comprises magnesium. There are numerous materials in the electromotive series which are anodic to iron. However, some of such materials are too active in water and would be consumed so rapidly as to be impractical for present purposes. Other such materials, including zinc, have a low operating efliciency and the protective current flow which they are capable of producing under many conditions would be below the minimum to insure complete protection against corrosion, and this would be particularly true where an external resistance is to be employed in the circuit between the sacrificial anode and the cathodic metal surface to be protected. Such operating ineificiency in part results from a low potential diiference between such metals and iron but also results from the tendency of the metals to polarize in an electrolyte solution. Such polarization materially reduces the effective protective current. considered unsatisfactory for this reason. Again, various metals, particularly when containing impurities, are subject to local battery action, one type of polarization, between different surface areas thereof in an electrolyte solution which causes them to be consumed too rapidly to make them useful for a sacrificial anode and the local current flow serves no useful function in the protection of the tank. While magnesium is subject to a certain amount of local battery action which hastens its corrosion and useful life, it undergoes very little polarization of other types and is well adapted to ensure adequate current flow to protect the tank when employed with as well as without a substantial resistance in conjunction therewith.

In the drawings:

Figure l is a view in vertical section through of cylindrical shape having mounted therein a device embodying my invention;

Figure 2 is a fragmentary top plan view thereof showing certain parts only;

Figure 3 is a fragmentary view taken on the line 33 of Fig. 2;

Figure 4 is a fragmentary view of the bottom portion of an element embodying my invention;

Figure 5 is a view in vertical section taken through a domestic hot water tank and including in modified form an anodic element embodying my invention Figure 6 is a fragmentary view showing only the top end of a tank end of a still further modification of anodic invention; and

Figure 7 is a fragmentary view showing the upper part of the tank and of the support for the anodic elements shown in Figure 5 of the drawings.

I have illustrated a domestic hot water tank I I as of elongated shape and of cylindrical trans- Zinc is f 4 verse section and provided with supporting means l3 and a cold water inlet l5 at the bottom of the tank, as well as a hot water outlet pipe II, the latter being connected to the tank at the upper end thereof. The inner end of cold water inlet pipe I 5 is covered by a perforate baffle member [9 of metal which I have shown, for purposes of illustration, as being of circular shape and of arcuate section.

The hot water outlet pipe I! may be threaded into a fitting 2! of T-shape, one end of which is screwed into an opening in the top of the tank while the upper end thereof is closed by a plug 23, which plug is adapted to receive a metallic suspending rod and the anodic element 21 now to be described.

This element 21 includes more particularly a block, preferably in the form of a magnesium rod 29. Both ends of this rod, which is shown as somewhat shorter than the axial or longitudinal dimension of the tank itself, is made of reduced size and screw threaded, as shown at 3! and 33 in Figs. 3 and 4 of the drawings. I do not desire to be limited to a rod form of block, but I have obtained very good results in the use of such kind of members in domestic hot water tanks made of ferrous metal.

I provide members 35 of electric-insulating material, which may consist of a molded composition which will withstand the acid, alkaline or saline waters to which they may be subjected when in use in a tank, or they may be made of ceramic or vitreous material. Each member is provided with a tubular insert or thimble 31 which is provided with internal screw threads and which are electrically connected to the respective ends of a sealed-in resistor member 39, which may be made of Nichrome or any other suitable material adapted for the purpose and which has a predetermined ohmic resistance as hereafter more fully explained.

The suspending rod 25, as was hereinbefore noted, has screw threaded engagement at its upper end (in a vertically-extending hot water tank) with the plug 23, while its lower end fits into and has screw threaded engagement with one of the thimbles 3'5, while the lower thimble 31 in the upper member 35 is engaged by the reduced end portion 3| of the rod 29.

I provide a similar member 35 at the lower end of the rod, one thimble or tubular insert 31 of which has screw threaded engagement with reduced end portion 33 of rod 29, while the lower thimble 31 is engaged by the upper end of a short pin M which has mounted thereon a washer 43 and a coil spring 45 extending between the tubular insert 31 and the lower end of the member 35 and the washer 43, the washer being normally biased along the pin or rod ll into engagement with a stop pin 41 fixed near the lower end of rod 4|. When the anodic element structure 27 is in its normal operative position in a hot water tank of the kind shown in Fig. l, the rod ti extends through an opening 49 in baffle [9, this opening 49 being in substantial alignment with the cold water inlet pipe [5. It will be noted that the anti-corrosion element 21 will therefore be substantially coaxial with the cylindrical tank II for a purpose to be hereinafter referred to. While I have shown a single corrosion-preventing element only, I do not desire to be limited thereto and may use a plurality of such elements peripherally spaced from each other and on a circle of predetermined but relatively small diameter.

In case the tank is filled with water which, due

require replacement in six months or a year or two. The operating life of the anode protection of the tank can be prolonged through the addition of one or more resistor elements as previously explained. Furthermore, the anode life and resistor value are interrelated and vary directly with one another. The resistor value required to provide a selected minimum life for a particular anode can, at least approximately, be readily predetermined, and conversely, it can be determined what the minimum life of anode will be when using a resistor of a particularly selected value.

The life of the anode and the value of the external resistance depend on a number of factors. The higher the total current flow from the anode, both protective current flow to the tank and the local flow under battery action between different areas of the anode, the more rapidly will the anode go into solution and the shorter its life. Hence, it is desirable to use as high a value external resistor as practical to ensure not less than the minimum protective current flow to the tank necessary for complete protection against corrosion. The efiect of battery action is quite appreciable and causes the anode to be consumed in less than half the life expectancy of the anode if determined theoretically only on the basis of the current flow to the tank. While the shortening of the life of the anode by battery action is not definitely known, it is here assumed, to be on the safe side, that battery action reduces the life of the anode by 65% or, to state the matter conversely, that the anode will be consumed in 35% of its theoretical life expectancy.

The protective current is determined by five factors. One is the potential difference between the anode and iron and for magnesium this is taken as 1.43 volts. Another factor is the specific conductance of the Water which will vary considerably with waters of different hardness and softness. The protective current will further be determined by the internal resistance of the water path between the anode and the surface of the tank, and this in turn depends upon the} specific conductance of the water and the diner- :ence in dimensions of the tank and the anode and upon the temperature. The resistance of solutions of electrolytes declines at about the rate of 1% for 1 F increase in temperature. The other factor is the value of the external resistor which is in series with the internal resistance of the tank, and the sum of which is the total resistance. The adverse effect of polarization of the magnesium anode is ignored because it would be substantially negligible as long as the pH is below 12.5, which would be true for any known domestic water supply.

The unit consumption rate of the anode metal in grams per ampere hour being expressable both in terms of weight and time and in terms of current and anode metal electrochemical equivalent liEI RQf E I-T or T= (R1132) tance between 0.33 10 to 16.5X1O

where R1=value of the internal water resistance Rz=value of resistance in ohms of the resistor E=the potential diiference in volts between the anodic metal and tank metal (1.43)

Eq=electrochemical equivalent of magnesium in grams per ampere hour (.447)

T=years of anode life, expressed in hours (8760 hours per year) W=weight of anode in grams, or in pounds times The value of the internal resistance R1 for any given operating temperature can be determined approximately for any given water from the tank and anode dimensions and the specific conductance of the water for average tank. Assuming a tank 39 long and 15.75 inside diameter and a co-axial magnesium anodic rod 1.575 in diameter, the internal resistance of the tank will run roughly from 112 ohms to 2 ohms at 65 F. for waters varying in hardness from 20 p. p. m. to 1000 p. p. m. and varying in specific conduc- If the temperature is 167 F. the internal resistance will be 37% of its value at 65 F.

In the formula above, T represents the theoretical life expectancy of the magnesium anode in the absence of battery action. Since over 50% of the consumption of the anode is due to local battery action the value found for T must be reduced by at least that amount. To ensure against over-calculation, it is best to assume that the actual life expectancy of the anode is about 35% of T.

The value of the external resistance R2 may be as low as 5 ohms, or preferably 10 ohms as a practical minimum, but unless the water resistance R1 is relatively high, the rate of consumption at such value would be far greater than necessary to ensure minimum protective current. I normally prefer to employ a resistor having a value ranging from to 200 ohms, say one of ohms, for general usage as this range is suificient to ensure adequate potential difference and relatively long tank protection without replacement of the anode, and at the same time provides a substantial margin of safety to ensure an adequate current flow for complete tank protection, under widely different conditions of Water resistance and taking into account the average temperature of the water over a yearly period. While the eifective water resistance increases with tank size, because of greater distance between the anode and tank wall, as well as with the purity of the water so that a given anode employed with a resistor of predetermined value will have a longer life the larger the tank, the difference in diameter of the more commonly used sizes of tanks for domestic water, at least those used in the household, is not sufficiently great to materially change the water resistance. Thus it is possible to employ a standardized resistor in the range above noted for the usual domestic hot watertank of 50 gallons and larger tanks up to a capacity of at least 150 gallons or 200 gallons. In the case of extremely small tanks it would be desirable to increase the resistance value, and in the case of abnormally large tanks to use a lower resistance value in order to obtain a similar predetermined operating life for the anode. In hot water tanks under average conditions a magnesium anode of two pounds, or thereabouts, will have an actual life expectancy as high as 15 years or more. Even .where such A assess-a an; anode:- is: used. the absence 01 an; extemal resistor it have a: useful lifevoi several years on filUI'GUHdGYfEVOI'QbIG water "conditions Where the tank is: provided with. a protective 'z-i'nc'lining such lining: is cathodic relative to the magnesium anode While being-'anodic relative-to the ferrous'tanh metal and in the: absence"v of penforations: in the lining the: flow of cuiirent between the anode and coating will be: somewhat less, with a Mg-Zn potential; difieren'ce: of 1.11, than: between the anode and: an uncoated". fenrous tank wall with a' Mgi-Fe potential. difference of 1143-. Accordingly, in the. preceding formula Ei may be taken as the potential difference; L11, bet-ween the anode and zinc coating: insteacli of bel'lllleeli the anode and iron wall for a; zinc. lined tan For reasons of initial and: replacement: cost; it

undesirable to employ protective anodes. of

substantial diameter, although the thicken the anode the greater the amount of. material. avail able therein for oonsun'iption, and thei'longer its useful life; I ordinarily employ an. anode of between one-half inch and two inches in diameten; most commonly one (it three quarters of an inch. Tdinsure full protectionio't the bottom of the tank the length of the anodeshould be such that the distance between the" lower end of. the anode and tank bottom is no greater than the radial distance between the anode andv the tank. The length will be determined. by the. length of the tank. It Will? be: apparent for: reasons allready explained that; by using acurrentreducin resistor-'- in conjunction. with the: anode a small size anode will have an operatingtlife as long, or even longer, than an anodeof greater size connected: to the tank in the absence of' a: resistor underequivalent conditions In other'words, the

upperen'd is adapted/toreceivea-nut- 53 having 1 an opening into which a hotv water outlet pipe 55 maybe screwed. The lower end portion of bushing; 5| is provided with a: flat internal shoul der' 51, the lower end of: the bushi' ng'mayreceive a tubular spacer 59 of electric-insulating material. A flat washer B I of electric-insulating niaterial,.- is adaptedto rest upon the shoulder 51 and the upper end: 63' of a shortanodic rod of magnesium is adapted. to fit: in the elongated washer or bushing 59 in a; fluid-tight manner and tote held therein by a nut 61, the manner shown more particularly Fig. 7 at the draw ings'.

I provide a resistor member 69 of anye siredtype, such as a small wireof' suitable resistor inaterial, one end ofw'hich may be held? by a short machinescrew H against the upper end of portion iii, while the other end of the resistor may be electrically connected the bushing 5 by" any suitable meanssuch as soldering or T Brazing; The bushing 5i is provided an n a plui'ality of laterally extendihg openings 13 therein to permit of the outflow of hot water intoand through outlet pipe55.

I- may use connection with the upper end member: 9:" plurality: of pivntallyl connected l portions: E5: in. the: shapeout magnesium rodslhaving tongue and slot connections with each other through a pin 17. As shown in; the brokemlihes im Eigz. 5 of: the: drawings, im case the tank; is laid on -its. side dimingsliipmentzor at other time,

the pivotall-yf comected sections: 1.5 will not. be

.suhj eoted to an undue str-alm causedv by: the un- =suppontedi thereof, since. at least: some: of these sections: may: rest upon the? tank: walla itself when. the. tank: is. in: a horizontal? positiom.

Reterri-nginow to; Fig: 6 oi the? drawingnli have there illustrated a still. further modification ofi'a corrosionepreventing: element. in which a; shout pipe: section: M be?v screwed into-the cover of tank t9; the uppen end; of: section. 19 beingscrew threaded lice receive: a. pipe fitting; whil'ewthezlower end. thereof; may have: art inner' shouldermember: upon: which; a perforated: inetalbushingi 83- is: adapted; to rest; Th bushing: 83- is. provided with a central; spherical: seat 85 on: whichthe upper enlarged sphericafl end 8101i 21: suspending. and

supporting rod: 89 is adapted to rest: The lower stalled: and highlyeffective meansfor itsintendjed: purpose. to not: only reduce but substantially entirely" prevent dissociation and corrosion of the: inner surface ot' a ferrous metal: tank, irrespective. oii whether the? inner surface of: the tank is coated with zinc or not; It further provides arianodic rod: which can be, but: preferably. is not cotmected; directly to the tank, but through a resistor, which iselectrically insul'atedtront the changing water in the tank. Ilhe ohmic resistance of the resistor relatively high, so that: I

, obtain: protection by? metering the current new.

resistor has too high an: ohmic resistant reduces the wrrent flow to a value: which will not tully' protect the because too few anodic ions are flowing to prevent the iron ion from flowing: A

anodic" rod or member may be secured by amounting to the side wall oi the tank; and may" extend; crosswise instead of lengthwise", if desired.

13' wish to point out that while I have illustrated and described aparticular form of not water tank, which is mostfreouentlyr'used in do me'stic hot water ins-taliations, my invention is not limited thereto its broader aspects.- Should the shape of the tank; and: particularly of its interior' suriace, be quite differentfrom that shown the drawings; my invention preierably; but notneoe'ssaril-y; contemplates the use of as corro si'on p'reventing anodic member of a shape sym' metrical tothat of the. inside surface of the tank but of much smaller outer surface area.

While 13' have illustrated and described specific embodiments of invention,- I do not desireto be limited thereto, since all modifications com:- ing clearly within the: scope of the appended claims are to be considered as being covered. thereby-L V This application is a continuation of my co pending application, Seri'ai No. 568,360, filed December' 1 5, i944, now abandoned which: in tum 1 l is a continuation-impart of my copending application, Serial No. 356,622, filed September 13, 1940 (now abandoned).

I claim as my invention:

1. The combination with a ferrous metal dmestic hot water tank in which cold water supplied from any of the conventionally available water sources is recurrently input and heated, and from which hot water is withdrawn at recurrent times and in varying amount according to demand, of anti-corrosion means for protecting the tank interior against corrosion comprising an elongated sacrificial magnesium metal anode of substantially smaller cross-section than the tank located within the tank to be surrounded by the tank water and relatively distant from areas of the tank to be protected, and electrically conductive means connecting the anode to the tank and adaptin the anode to supply a galvanic current fiow to areas of the tank metal when exposed to contact with the tank water.

2. The combination with a ferrous metal domestic hot water tank in which cold water supplied from any of the conventionally available water sources is recurrently input and heated, and from which hot water is withdrawn at recurrent times and in varying amount according to demand, of anti-corrosion means for protecting the tank interior against corrosion comprising a zinc lining on the interior of the tank, an elongated sacrificial magnesium metal anode of substantially smaller cross-section than the tank located in the tank to be surrounded by the tank water and relatively distant from the tank interior, and. electrically conductive means connecting the anode to the tank and adapting the anode to supply galvanic current fiow to the zinc lining and to any areas of the tank metal exposed to contact with the tank water.

3. The combination with a ferrous metal domestic hot water tank in which cold water supplied from any of the conventionally available water sources is recurrently input and heated, and from which hot water is withdrawn at recurrent times and in varying amount according to demand, of anti-corrosion means for protecting the tank interior against corrosion comprising an elongated sacrificial magnesium metal anode of substantially smaller cross-section than the tank located within the tank to be surrounded by the tank water and relatively distant from areas of the tank to be protected, and electrically conductive means including an electrical resistor element connecting the anode to the tank and adapting the anode to supply a galvanic current flow to areas of the tank metal when exposed to contact with the tank water.

4. Th combination of claim 3 wherein the electrical resistor element has a value within the range of 5 ohms to 200 ohms.

5. The combination of claim 3 wherein the electrical resistor element is located in the tank and further including a water impervious housing encasing and protecting said electrical resistor element against contact by tank water.

6. The combination with a ferrous metal domestic hot water tank in which cold water supplied from any of the conventionally available water sources is recurrently input and heated, and from which hot'water is withdrawn at recurrent times and in varying amount according to demand, of anti-corrosion means for protecting the tank interior against corrosion comprising a zinc lining on the interior of the tank, an elongated sacrificial magnesium metal anode. of sub-- stantially smaller cross-section than the tank located in the tank to be surrounded by the tank water and relatively distant from the tank interior, and electrically conductive means including an electrical resistor connecting the anode to the tank and adapting the anode to supply galvanic current flow to the zinc lining and to any areas of the tank metal exposed to contact with the tank water.

7. The combination of claim 6 wherein the electrical resistor element has a value within the range of 5 ohms to 200 ohms.

8. The combination with a ferrous metal domestic hot water tank in which cold water supplied from any of the conventionally available water sources of ranging composition as to corrosion action is recurrently input and heated, and from which hot water is withdrawn at recurrent times and in varying amount according to demand, said tank having a wall opening, of anticorrosion means for protecting the tank interior against corrosion comprising a metal plug constituting a removable closure for said tank wall opening and having electrically conductive connection with the tank, an elongated sacrificial magnesium metal anode of substantially smaller cross-section than the tank and adapted to pass through said tank wall opening, said anode being insulated from the plug by an electrical insulator and supported by the plug within the tank to be surrounded by the tank water and relatively distant from areas of the tank to be protected, and an electrical resistor element supported by the plug and electrically interconnecting the anode and the plug and adapting the anode to supply a galvanic current now to areas of the tank metal when exposed to contact with the tank water.

9. The combination with a ferrous metal domestic hot water tank in which cold water supplied from any of the conventionally available water sources is recurrently input and heated, and from which hot water is withdrawn at recurrent times and in varying amount according to demand, said tank having a wall opening, of anticorrosion means for protecting the tank interior against corrosion comprising a plug constituting a removable closure for said tank wall opening and extending into the tank, an elongated sacrificial magnesium metal anode of substantially smaller cross-section than the tank, and adapted to pass through said tank wall opening, said anode being supported by the plug within the tank to be surrounded by the tank water and relatively distant from areas of the tank to be protected, said plug being formed of water im pervious material and with a hollow interior closed to exposure to the tank water, and an electrical resistor element located in the hollow interior of the plug for protection against tank water through which the anode member is electrically connected to the tank and adapting the anode to supply a galvanic current flow to areas of the tank metal when exposed to contact with the tank water.

10. An anti-corrosion unit for protecting the interior of ferrous metal domestic hot water tanks in which cold water is supplied from any conventionally available water source is recurrently input and heated, and from which water is withdrawn at recurrent times and in varying amounts according to demand, said unit being adapted for tank installation as an assembly unit and comprising a closure and supporting plug adapted to be removably mounted in a wall opening of such a tank, an elongated sacrificial magnesium metal anode of smaller cross-section than the plug supported at one end by the plug and adapted to be located within a tank to be surrounded by the tank water relatively distant from interior areas to be protected, electric insulating means insulating the anode from the plug and an electrical resistor element supported by the plug for electrically interconnecting the anode and a tank, said element having a resistance within a range of 5 ohms to 200 ohms.

11. An anti-corrosion unit for protecting the interior of upstanding cylindrical ferrous metal domestic hot water tanks in which cold water is supplied from any conventionally available water sources is recurrently input and heated, and from which water is withdrawn at recurrent times and in varying amounts according to demand, said unit comprising a metal closure and supporting plug adapted to be removably mounted in a top wall opening of such a tank, an elongated sacrificial magnesium metal anode of smaller crosssection than the plug supported at one end by the plug and adapted, when the plug is mounted in a tank, to be suspended vertically within such tank surrounded by tank water with the anode axis in parallel with the cylindrical tank wall, electric insulating means insulating the anode from the plug and an electrical resistor element supported by the plug electrically interconnecting the anode and the plug, said element having a resistance within the range of 5 ohms to 200 ohms.

12. In an anodically protected hot water heater system of the class wherein a metal hot water tank acts as a cathode and a metal anode is projected into the tank and electrically connected 7 to the tank; the combination with the anode of a metal, water outlet fitting for supporting the anode and electrically connecting it with the tank, the fitting having an axial water passage therethrough, connecting means at the outer end of the fitting for connecting it with piping, external threads around the fitting inwardly of the connecting means, for supporting the fitting on the tank and electrically connecting the fitting and tank, the fitting having a lateral opening inwardly of the external threads, leading from the axial passage through the surface of the fitting, and means mounting the anode on the fitting, said means being below the lateral opening in the fitting and the parts of the assembly inwardly of the external threads on the fitting being no larger in overall diameter than the said threaded portion of the fitting whereby the assembly as a unit may be inserted through an opening in the end of the hot water tank and threadedly attached and electrically connected thereto.

- 13. An anti-corrosion unit for protecting the interior of ferrous metal domestic hot water tanks comprising a metal outlet pipe fitting and an elongated sacrificial magnesium metal anode electrically connected to and adapted to be supported by the fitting within a hot water tank, the fitting having an axial water passage leading from a first or outer end of the fitting inwardly and having a. lateral water delivery opening connecting with the passage and leading through the side surface of the fitting and located inwardly of the outer end of the fitting, connecting means at the outer end of the fitting for connection of the fitting with piping, external threads around the fitting inwardly from said connecting means, for connection of the unit in a threaded wall opening of a hot water tank, attaching means connecting one end of the anode to the fitting, said attaching means being inwardly of the lateral open- 111g in the fitting, means closing the axial passage below the lateral opening in the tubular member, and the parts of the unit inwardly of the external threads on the fitting being no larger in overall diameter than the said threaded portion of the fitting whereby the unit may be inserted through a threaded wall opening of a hot water tank, threadedly attached and electrically connected to the wall.

14. An anti-corrosion unit for protecting the interior of ferrous metal domestic hot water tanks comprising a metal outlet pipe fitting and an elongated sacrificial magnesium metal anode electrically connected to and adapted to be supported by the fitting within a hot water tank, the fitting having an axial water passage leading from a first or outer end of the fitting inwardly and having a lateral water delivery opening connecting with the passage and leading through the side surface of the fitting and located inwardly of the outer end of the fitting, connecting means at the outer end of the fitting for connection of the fitting with piping, external threads around the fitting inwardly from said connecting means, for connection of the unit in a threaded wall opening of a hot water tank, a partition across the fitting inwardly of the lateral opening, the inner end of the fitting having a socket extending thereinto, coaxial with the axial passage, the anode having an upper end located in the socket and means securing the anode tightly and rigidly in the socket, and the parts of the fitting and the anode inwardly of the external threads on the fitting being no larger than the said external threads whereby the said parts may be inserted through a threaded wall opening of a hot water tank, threadedly attached and electrically connected to the, wall.

CLARK M. O'STERHELD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 999,108 Hickey July 25, 1911 1,506,306 Kirkaldy Aug. 26, 1924 1,512,557 Mills Oct. 21, 1924 1,514,903 Gush Nov. 11, 1924- 2,029,5'70 Kasarjian Feb. 4, 1936 2,343,440 Andrus Mar. 7, 1944 2,459,123 Bates Jan. 11, 1949 FOREIGN PATENTS Number Country Date 386,772 Canada Feb. 6, 1940 631,137 Germany June 12, 1938 OTHER REFERENCES Status of Cathodic Protection of Pipe Lines in 1941, by Logan, Nov. 3, 1941, page 6.

"Corrosion of Metals," by Evans (1924), pages 186, 187.

Hackhs Chemical Dictionary, second edition (1937), page 315.

Corrosion and Material Protection," July- August 1947, pages 12-15.

Metallic Corrosion, Passivity, and Protection, by Evans (1946), pages 526, 527.

Corrosion Handbook, by Uhlig (1948), pages 814, 1134.

Handbook 01 Chemistry and Physics, 24th edition (1940) pages 390, 391, 438, 439, 462, 463, 486, 487, 518, 519. 

1. THE COMBINATION WITH A FERROUS METAL DOMESTIC HOT WATER TANK IN WHICH COLD WATER SUPPLIED FROM ANY OF THE CONVENTIONALLY AVAILABLE WATER SOURCES IS RECURRENTLY INPUT AND HEATED, AND FROM WHICH HOT WATER IS WITHDRAWN AT RECURRENT TIMES AND IN VARYING AMOUNT ACCORDING TO DEMAND, OF ANTI-CORROSION MEANS FOR PROTECTING THE TANK INTERIOR AGAINST CORROSION COMPRISING AN ELONGATED SACRIFICAL MAGNESIUM METAL ANODE OF SUBSTANTIALLY SMALLER CROSS-SECTION THAN THE TANK LOCATED WITHIN THE TANK TO BE SURROUNDED BY THE TANK WATER AND RELATIVELY DISTANT FROM AREAS OF THE TANK TO BE PROTECTED, AND ELECTRICALLY CONDUCTIVE MEANS CONNECTING THE ANODE TO THE TANK AND ADAPTING THE ANODE TO SUPPLY A GALVANIC CURRENT FLOW TO AREA OF THE TANK METAL WHEN EXPOSED TO CONTACT WITH THE TANK WATER. 